1. Technical Field
The present disclosure relates to a light emitting diode (LED) and method for making the same.
2. Description of Related Art
In recent years, highly efficient LEDs made with GaN-based semiconductors have become widely used in different technologies, such as in display devices, large electronic bill boards, street lights, car lights, and other illumination applications. LEDs are environmentally friendly, long working life, and low power consumption.
A conventional LED commonly includes an N-type semiconductor layer, a P-type semiconductor layer, an active layer, an N-type electrode, and a P-type electrode. The active layer is located between the N-type semiconductor layer and the P-type semiconductor layer. The P-type electrode is located on the P-type semiconductor layer. The N-type electrode is located on the N-type semiconductor layer. Typically, the P-type electrode is transparent. In operation, a positive voltage and a negative voltage are applied respectively to the P-type semiconductor layer and the N-type semiconductor layer. Thus, cavities in the P-type semiconductor layer and electrons in the N-type semiconductor layer can enter the active layer and combine with each other to emit visible light.
However, extraction efficiency of LEDs is low for the following reasons: first, the typical semiconductor materials have a higher refraction index than that of air, therefore, large-angle lights emitted from the active layer may be internally reflected in LEDs, so that a large portion of the lights emitted from the active layer will remain in the LEDs; second, the current is limited under the P-type electrode, so that the conduction of the current along a direction away from the P-type electrode is weaken, thus the lights emitted from the active layer is reduced. The extraction efficiency of LEDs is low so that the heat produced in the LEDs is remained in the inner of the LED. Therefore, the property of the semiconductor materials is damaged and the life span of the LED is shorter. As a result, the large-scale application of the LEDs is affected.
What is needed, therefore, is a LED and a method for making the same, which can overcome the above-described shortcomings.